Section 3 overview of potential threats

Transcription

Section 3 Overview of potential threats
Freshwater systems require special consideration in regards to threats, as it is not only local and obvious
changes to habitat and species introductions that can cause impacts. The fluid nature of water means
that freshwater habitats are often connected within broader networks (e.g. streams) and with terrestrial
habitat. As a result threats from one area can be transmitted elsewhere, especially downstream, such
that the cumulative result of practices in or around waterways or catchments can impact aquatic
habitats in an area (e.g. Figure 13).
A range of documents provide background on threats to freshwater fishes and habitats in different
parts of Australia12,22,31,74,87,236,237. The intention of this section is to summarise and develop a list of potential
threats relevant to South Australia (Table 3), reinforced with local examples and as a summation from
individual species accounts. While a list of threat categories is provided, a particular process rarely acts
on its own and will likely have consequences of species decline interlinked with other threats overlapping
on different spatial and time scales. For example habitat degradation, introduced species and local
pollution would become more severe with loss of flow and during warmer periods. Some threats may
have obvious and immediate impacts, while others take time to become evident (i.e. lag time) or are
masked until a particular threshold is reached. The list of threats is not necessarily reflective of an order
of severity. However, hydrological alteration is considered the primary or underlying threat to fish habitat
and communities across South Australia.
Abstraction of low flows, habitat loss, fishing pressure
Locks and weirs, siltation, introduced fish and disease
Major hydrological
development, increasing
agricultural intensity
(pesticides, fertilisers), further
introduced species
Slight improvement with
restoration initiatives
Critical low flow
and water levels
Figure 13. Decline of the SA River Murray fish community since European settlement. The model is
developed after the MDBA Native Fish Strategy which considered decline in species diversity and
abundance of native fish to have reached 10% of pre-European levels for the MDB by 2003. The green
bar represents the target for restoration under the same strategy236.
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2009 Action Plan For South Australian Freshwater Fishes
Further flow decline, Barrages, heavy fishing
Table 3. Potential threats to freshwater fishes in South Australia.
Threat category
Examples causes (processes)
1. Hydrological (flow) alteration
a) Loss of water from a system/habitat
Reservoirs,
Farm dams, pumping surface and groundwater, drainage, climate
change, plantations
b) Altered flow seasonality and
variability
Provision for irrigation
(i.e. seasonal reversal), dams (e.g. delay the onset of flow periods),
land clearance, climate change
2. Habitat loss and degradation
a) Removal and alteration of habitat
(broad)
Reduced flow, drainage, damming, channelisation, river engineering,
levees (floodplain loss), urbanisation
b) Removal and damage of riparian
vegetation
Land clearance, stock access, urban/rural development
c) Loss of instream cover
Desnagging, dredging, siltation & overgrazing, altered hydrology,
removal of aquatic vegetation, exotic plants, algal growth (nutrients)
d) Artificial barriers to fish movement
and gene flow
Physical structures (e.g. weirs, dam walls, road culverts), biological
barriers (e.g. loss of intervening habitat, predators, water quality, high
velocity)
3. Lowered water quality
a) Fish kills
Toxic substances (e.g. chemicals & pollutants), reduced flow,
eutrophication, suspended sediments, temperature
b) Sub-lethal responses (e.g. reduced
spawning or feeding ability)
Salinity, reduced dissolved oxygen, altered temperature (e.g. thermal
pollution, loss of flow and shade, climate change)
c) Reduced habitat quality
Sedimentation, nutrient input (algal growth)
4. Alien species & stocking (biological pollution)
a) Biological impacts (competition,
predation, aggression, habitat
modification)
Introduction and/or establishment of exotic and translocated native
species
b) Transfer of disease and parasites
Introduction of exotic and translocated native species, discarded
aquarium fishes and plants, inter-basin transfer and movement of
materials, equipment and vegetation
c) Genetic impacts
Inappropriate translocation and stockings (e.g. mass releases,
hybridisation)
5. Exploitation or use
a) Reduced abundance and
reproductive potential
Past and present fishing pressure and aquarium trade (recreational,
commercial and illegal)
b) Trophic cascades and altered states
Selective removal of a keystone or prey species.
6. Population decline
a) Loss of genetic diversity & reduced
ability to adapt to change
Previous unnatural range contractions, ongoing population
bottlenecks (e.g. exotic predatory species), fragmentation
b) Restricted range and/or small
populations
Restricted range and/or small populations
Vulnerable to lag effects, new threats, change and stochastic events,
genetic problems (e.g. inbreeding)
c) Failure to include fishes in
management and planning
Lack of: knowledge, monitoring/research, awareness (government &
community) and appropriate legislation
7. Climate change
a) Change in habitat and flow
Temperature increases, decreased and altered rainfall
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3.1. HYDROLOGICAL (FLOW) ALTERATION
Hydrology (processes involving water) is the main driver to the presence, nature and dynamics of aquatic
habitats. The hydrology of different habitat types or systems can vary considerably, depending on the
source of water, position in a landscape and local climate and geology. Sources of water include (a)
local rainfall and runoff, (b) linear or longitudinal flows (e.g. stream flow from headwaters to the sea), (c)
lateral (outward) linkages such as the inundation of edge, wetland or floodplain habitat, and (d) vertical
interactions with groundwater. All of these linkages can vary in their frequency, magnitude, duration,
timing and rate of change to be temporally variable. Aquatic biota may also rely on particular aspects
like flow for breeding, movement and survival, or have innate responses to components of natural water
regimes such as flooding and disturbance238,239.
Given the generally warm climate combined with low to moderate or variable rainfall in South Australia,
the presence and dynamics of water is considered of primary importance in maintaining habitats for
fishes. Many important fish habitats or critical summer refuges would simply not exist if not for river flow
from higher rainfall areas or expression from groundwater sources (e.g. springs). Hydrological alterations
relate to two main problems: loss of water and altered flow patterns.
(A) LOSS OF WATER Loss of water can result from any practice which removes water directly or impacts
a source of water and thus eliminates or alters habitat at large and/or micro scales (e.g. the drying of a
stream reach and loss of pools). A significant problem occurs with drying of habitat for small populations,
and is most critical when water is already scarce during dry seasons or extended periods where human
use tends to exacerbate already low levels. For example recent (last 10 years) widespread drying of once
permanent fish habitat in streams and springs has been witnessed in areas of the Eastern Mount Lofty
Ranges25,51. The recent prolonged period of low rainfall has also highlighted critical deficiencies in water
management to maintain fish habitat in the Lower Murray114,129 and South East94.
In addition to drying of habitat, reduced flow volume can lead to reduced flushing of salts, altered
geomorphology (e.g. reduction in channel depth, encroachment of reeds), reduced aquifer recharge
and direct ecological implications. Loss of water can also reduce the magnitude of particular flow events
limiting the size of floods and the amount of wetted habitat. For example, floods on the River Murray are
now much fewer in frequency and smaller than which occurred naturally185.
Direct removal can include:
• Deliberate drying of wetlands for management or during works along or in streams aquatic habitat (fish
need water).
• Direct pumping from aquatic habitat impacts overall water availability and can increase the risks of
habitat drying eliminating local flows and habitat components (i.e. lower water levels) or lead to total
habitat loss. Again this can be an especial problem in dry periods and for localised populations.
Loss of water sources (linkages) can be caused by:
• Large dams and reservoirs capture water and limit the volume received by downstream environments
(and alter the nature of flows and habitat downstream –see altered variability). Large dams impact
most major river and stream systems in South Australia with the current exception being the
unregulated Lake Eyre Basin. The River Murray now only receives one third of its natural flow volume
into South Australia due to upstream dams and diversions (e.g. irrigation186,241)and there is an extensive
water supply network in the Western Mount Lofty Ranges involving numerous reservoirs including
Myponga, Millbrook, Warren, South Para, Mt Bold, Kangaroo Creek and Little Para.
• Farm dams can have local and cumulative impacts within catchments contributing to overall loss of
water from a system through capturing (abstracting) surface water. For example there are moderate
to very high levels of farm dams in most areas of the Mount Lofty Ranges, with this form of water
resource development escalating rapidly (e.g. doubling of storage volume in some catchments) in the
last 10-15 years. In the Marne River Catchment for example, more than 640 dams capture on average
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• Drainage and conversion to alternative uses is a special problem for wetlands and floodplains either
altering hydrology by limiting or removing wetting (see examples in Habitat loss).
20% of water destined for stream flow, with this percentage of capture much higher in drier years and
at certain times of year like summer when important small flows are virtually eliminated149. Similarly
farm dams have been calculated to reduce the median summer flows, important for maintaining
habitat presence and condition (e.g. cool oxygenated pools in Mediterranean type climates), by up to
72% in some years150 (see also flow seasonality).
• Groundwater extraction is an underestimated and latent problem because groundwater sources
(aquifers) are not directly obvious and in many cases not well known. Consumptive use of groundwater
may lead to one or a combination of rapid extermination of small reserves, interception of flows
destined for other areas or broader lowering of water tables, all of which may lead to reduction or
loss of groundwater expression to the surface (e.g. flow discharging from springs) or lowered surface
water levels where the two are interconnected. Because groundwater processes are often complex
interactions between historic influences and surface water recharge, such processes may operate over
long timelines. There is a particular danger of lag effects where impacts may not be evident for some
time, nor be readily reversible once problems are evident. Groundwater is often relied on by aquatic
biota during dry periods or in dry regions (e.g. desert mound springs, core refuges in the Mount Lofty
Ranges and unique spring fed habitats in the South East) and there is thus a high potential for conflict
with human consumptive use.
• Plantations are an emerging issue of water use due to the high density of trees (pine or Tasmanian
Bluegum) and high water demands by mature trees especially in small catchments/waterways and
areas of groundwater recharge. Water loss occurs through two processes: (1) plantations can act
as an umbrella capturing rainfall and reducing aquifer recharge or runoff into streams and wetlands
depending on the scale of the plantation relative to catchment area, and (2) plantations can be
water pumps that use groundwater with subsequent lowering of groundwater levels (e.g. by as much
as 9-10m depending on rainfall, plantation location and soil type). There is also potential habitat and
water quality issues from plantation processes including erosion, runoff and chemical use. Leaf litter
from plantations may have detrimental effects on water quality and in-stream processes when it
enters waterways.
• Climate change will result in altered patterns of rainfall, runoff and drought (see later).
(B) ALTERED FLOW PATTERNS Altered flow patterns are interlinked with water loss, but involve more subtle
hydrological alterations which change the nature of flow. Alterations of flow patterns can affect flow
seasonality or timing and variability. This in turn can affect habitat suitability and directly interfere with
species lifecycles.
Flow seasonality refers to the time of year flows occur, and local animals and plants are often tuned to
natural cycles by having seasonal cues for breeding and movement. Alterations in flow seasonality may
mean that flows start much later and do not link with appropriate times for fish spawning and movement
for example, and lead to longer periods of exposure to low water levels and reduced water quality (e.g.
temperature, dissolved oxygen, salt, pollutants). Altered timing of flow events (e.g. a shift from winter
dominated flow and floods may also be out of synchrony with natural cycles or biological response
impacting fish breeding and survival.
Natural variability in flows and water levels over time forms a part of ecosystem function and is thought to
promote higher native species diversity. Shifts away from natural rates of variation can thus be a threat.
Flows and flooding generates physical disturbance or fluctuation in habitats which can be important
for ecological function, and involve processes such as flushing sediment and cleaning underwater
surfaces, preventing the encroachment of reeds and diluting salts. Most native species have adapted to
natural variability (e.g. they move outward into riparian vegetation during floods, utilise different habitat
at different times of the year) while some exotic species like Gambusia and Carp are discouraged by
variability or alternately favoured by stable conditions. Rapid water level fluctuations could lead to
stranding of eggs or larval stages and unreliable habitat or cover for adults. At the other extreme stable
environments might encourage or favour habitat generalists and invasive species over rare species240.
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Major causes of altered flow patterns include:
• Regulation (weirs, barrages, large dams/reservoirs) provide the plethora of impacts relating to altered
flow patterns. Flow releases or overflow from large storages is unpredictable, commonly occurs during
unnatural times when irrigation demand is high (e.g. summer along the River Murray), and is often ‘all or
nothing’ where large bursts of water suddenly occur as an extreme disturbance (e.g. reservoir
overflow). The series of Locks and Weirs along the River Murray and Barrages maintain highly stable weir
pools as opposed to river habitat.
• Farm dams can have a large impact on seasonality by holding back or capturing runoff at the break
or end of seasons and thus delaying flows until dams can overflow.
• Instream works such as dredging, modifications of river banks, road crossing and other structures, can
drop water levels rapidly57 thus stranding eggs or juvenile stages and removing access to important
types of habitat (e.g. for spawning).
• Climate change may lead to altered rainfall patterns and timing reducing the onset of flow and
altering the timing and frequency of larger flow events for which biota might be unaccustomed
to (see later).
• Direct pumping (bottom left of photo) during a dry period, combined with reduced environmental
flows from abstraction in the catchment led to the drying for the first time of this pool on Dawson
Creek (2004) in the Mount Lofty Ranges, previous habitat of threatened Southern Pygmy Perch and
Mountain Galaxias.
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Hume Dam on the upper Murray,
part of the regulation picture
resulting in major reductions of
flow to South Australia
Direct pumping during a dry period,
combined with reduced environmental
flows from abstraction in the catchment
led to the drying for the first time of this
pool on Dawson Creek (2004) in the
Mount Lofty Ranges, previous habitat of
threatened Southern Pygmy Perch and
Mountain Galaxias
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3.2. HABITAT LOSS AND DEGRADATION
Fish habitat can range from broad scale suitability (e.g. stream, river, wetland) to local or microhabitat
requirements. Different species require habitat for a variety of reasons including:
• Cover from predators and competitors.
• Shelter from environmental conditions such as high flow velocity.
• Spawning structure or sites (e.g. hollows, submerged vegetation, gravel benches).
• Shade to maintain cool temperatures over warm periods.
• Food sources (e.g. aquatic and terrestrial invertebrates).
Cover or habitat components include submerged structures such as rocks, snags (woody debris) and
aquatic plants, fringing or emergent vegetation such as reeds and sedges, and overhanging terrestrial
vegetation.
Some species have more specialised requirements or reliance on cover than others, with differences also
within a species at different stages of their life cycle (juveniles and small species normally need higher
densities of cover). Habitat requirements can vary through time depending on different water levels and
types of flow, especially during floods when normally dry habitats are utilised to escape dislodgment and
unfavourable conditions (e.g. cover on river banks, floodplains).
Considering the different uses and roles of habitat, then not surprisingly habitat loss and degradation
can take many forms and vary greatly in impact severity. Impacts can be obvious from processes which
visibly directly alter habitat, but other changes may have more subtle impacts on the structure and
connectivity of habitats or alter conditions relied upon by fishes.
Diagram depicting different types of fish habitat: emergent and submerged aquatic vegetation, large
and small woody debris (snags) and overhanging vegetation (shade, input of organic matter, future snags
and source of terrestrial invertebrates) (B. McKenzie)
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(A) REMOVAL AND ALTERATION OF HABITAT (BROAD) Much broad scale change to river systems has
occurred since the advent of European settlement, whereby large areas of catchments have been
progressively cleared. Subsequent changes to the nature of flow and sediment inputs have occurred
with stream channel erosion, incision and siltation and are large scale issues transforming habitats in the
Mount Lofty Ranges for example.
A change in landuse to urban and semi-urban environments transfers parts of catchments to artificial
structure that changes the character and nature of waterways. Extensive changes have occurred in the
Adelaide region (Figure 14), as well as other regional centres.
Other landscape level changes include drainage and river transformation.
Prime examples include:
• A comprehensive and still expanding network of drains in the South East which has resulted in the loss
of over 90% of wetland habitats and alteration of most others23,203,204.
• The loss (>40% total) or alteration (at least 50% or remaining) of a large percentage of swamps on the
Fleurieu Peninsula (e.g. conversion to pasture)242.
• Levees along the River Murray between Wellington and Mannum which have transformed (removed
most swamp and wetland habitats.
Many aspects of habitat change can be related to altered hydrology (see 3.1) such as stream drying, loss
of flooding and access to fringing and wetland habitats.
(B) RIPARIAN VEGETATION Fringing terrestrial vegetation such as trees, shrubs and fringing water plants
(e.g. sedges and rushes) can provide the base of habitat and food chains via the input of woody
debris and living structure at both varying water levels. Hence buffers around streams and wetlands are
important. Vegetation can also influence physical conditions such as water quality via shade (cooler
temperatures in summer) and nutrient uptake or trapping silts.
Unrestricted stock access, land clearance and modifications for rural and urban development can
significantly alter stream habitats22,243. During dry periods, stock can reduce cover and also affect water
quality (especially oxygen levels) through wading and waste. In addition to the direct loss of cover, loss of
riparian and terrestrial vegetation can also alter the structure or geomorphology of areas. For example
trampled stream edges are unstable and more easily eroded leading to channelised environments
with high velocity and little cover. Stock access to aquatic habitats is still common place in most areas
of South Australia and heavy unregulated access is particularly likely to impact small sensitive habitats.
Many urban habitats are stripped of riparian vegetation when they are transformed or channelised,
especially in the Adelaide region (Torrens and Patawalonga catchments).
(C) LOSS OF INSTREAM COVER A decrease in the amount of instream cover available to fishes is often
related to the level of land clearing and local riparian clearance (i.e. decreased input of woody debris).
For example an extensive program was undertaken along the River Murray to remove large woody
debris (snags) and thus improve navigation conditions. Siltation (build up of fine silts and sand) can
smother underwater surfaces reducing physical cover such as rocks and suppressing plant growth.
Similarly, leaf fall from exotic trees and high nutrient levels, encouraging growth of filamentous algae or
dense floating plants (e.g. Duck Weed) which can also smother underwater surfaces.
Some physical activities are extremely disturbing to instream cover such as construction of road crossings,
removal of aquatic vegetation undertaken for improved recreation or industry, instream dams or other
works, dredging, and stream side development (e.g. infilling with dirt and rubbish). In the South East,
the maintenance of natural streams as drains provides regular physical disturbance to stream beds,
vegetation and banks57. Heavy stock access could also disturb instream cover, especially with large
hoofed animals in small or fragile environments. The highest likelihood of impact from the loss of instream
cover is in areas where sedentary and sensitive native fish occur, or for species that have particular
requirements for cover such as hollows for spawning and guarding eggs.
132
Unrestricted stock access can
reduce instream and bank
cover and lead to water quality
problems, especially during dry
periods (photo taken in the Lake
Eyre Basin)
133
(D) BARRIERS TO MOVEMENT AND MIGRATION Fish need to move between habitat sections for a variety
of reasons and at a variety of scales. Large scale movements are undertaken by diadromous species,
which require access between freshwater and estuarine/marine habitats at particular life stages (see
Figure 15), and potamodromous species, which undertake large movements within freshwater. For
example Murray-Darling Golden Perch tagged in South Australia around Renmark in the 1970s moved
hundreds and even thousands of kilometres upstream and downstream during periods of river flow162.
Other species may make smaller unidirectional or return movements for events such as spawning and
feeding to particular habitats (e.g. floodplains, stream headwaters) or dispersal and recolonisation from
refuges as part of regional populations. Even tiny species such as Carp Gudgeons and Dwarf Galaxias
are known to move upstream and between wetlands23,25,202.
Artificial barriers to fish movement are common in parts of South Australia and examples include:
• Reservoirs, dams and other major instream structures (e.g. barrages, locks and weirs).
• Instream farm dams or other structures.
• Smaller weirs including flow gauging stations.
• Levees (wetlands and floodplains).
• Elevated roads, culverts and crossings.
• Behavioural barriers such as darkened areas or inappropriate habitat (from habitat change).
• Physiological barrier such as high velocity flow or poor water quality areas.
• Biological pollution – presence of introduced predatory or aggressive fish.
In addition to direct blockage of upstream or lateral movement, fish concentrated below barriers are
exposed to predators, stress and disease. Downstream passage can also be affected or result in high
mortalities associated with falls over spillways or through highly turbulent areas.
While in the main artificial barriers to dispersal have a negative effect, it is worth noting that some fauna
rely on barriers to escape other threats such as predatory introduced fish. Natural barriers provide longterm isolation for some species free from competition with both native and introduced species and
introduction of fish into such areas can have impact on species biology, genetics and survival.
Figure 14. Example of major anthropogenic habitat changes to the Torrens and Patawalonga
catchments28.
134
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example of the anadromous Pouched Lamprey. Figure and text adapted from McDowall (1988)244.
135
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3.3. LOWERED WATER QUALITY
Water quality is a relatively complex combination of chemical and biological interactions in a
local environment with broader influences. For example, levels of dissolved oxygen, one of the key
water quality parameters, can be influenced by things like temperature, flow (aeration), suspended
solids, concentration of organic carbon, and biological/chemical oxygen demand (fish, plants,
algae, bacteria). Temperature in turn is governed by a variety of factors such as climate, water
source, local radiation or shade and pool characteristics such as depth and surface area. Flow is
further linked to water quality by diluting or distributing pollutants. Lowered water quality will have
different implications or act as triggers for different processes such as fish mortality (fish kills), sublethal responses, and generate flow on effects to habitat quality. Negative effects will vary widely
depending on fish condition, stress, species and age (size).
(A) FISH KILLS There are various potential causes of fish kills including natural events associated
with habitat drying (e.g. temporary fish populations die as Lake Eyre recedes after flooding).
Anthropogenic change can alter natural cycles of drying and water chemistry exacerbating
natural events. In particular loss or reduction in base flow which might buffer oxygen or temperature
levels, which can lead to suboptimal and ultimately lethal conditions25.
Other inputs (pollutants) in isolation or combination are potential causes of fish kills:
• Pesticides such as Endosulfan (an organochlorine) are known to be toxic to fish 245. Historically
the pesticides Dieldrin and DDT were thought to harm fish populations in South Australia176,202.
• Herbicides – in addition to impacting habitat (i.e. aimed to kill aquatic plants), these chemicals
may be toxic, particularly the wetting agents used to help dispersal.
• Other toxic substance include heavy metals, acidic conditions 60,246, ammonia, hydrogen
sulphide, winery waste and various industrial chemicals.
• High salinity and or temperatures can be above the tolerance of certain fishes.
• Turbidity (suspended solids) from runoff, instream or near stream works, can clog fishes gills and
reduce oxygen availability.
• High nutrient levels from urban or agricultural runoff combined with warm still conditions promote
blooms of algae and cyanobacteria (blue-greens) which can have a high demand for oxygen
resulting in eutrophication.
• In urban environments toxic substances, organic load and large bacterial loads (high oxygen
demand) occur with stormwater after rainfall, especially following dry warm periods. Both
aforementioned problems could be linked to irregular fish kills observed in the Torrens Lake in the
centre of Adelaide and Patawalonga Lake at Glenelg.
Disease may also cause mass mortality in fishes (see later).
Fish kills should be reported to the 24 hour FISHWATCH hotline on 1800 065 522.
(B) SUB-LETHAL RESPONSES The same factors involved in fish kills, but at sub-lethal levels, can impact
on the condition of fish and the ultimate survival or successful breeding of individuals or populations
in a chronic or cumulative way. Fish may be stressed, use extra energy or be unable to feed or
breathe normally when exposed to certain substances. The potential consequences include poor
fish condition and health (e.g. susceptible to disease and predators), increased abnormalities, poor
growth and shorter lifespan, reduced or failed spawning, and low survival of eggs and larvae.
(C) REDUCED HABITAT QUALITY Other aspects of water quality may influence the structure or nature
of aquatic habitats, linking together various other threat categories. For example un-naturally high
turbidity limiting light penetration may inhibit plant growth, fish feeding, fish behaviour and water
quality. Filamentous algae and suspended solids that settle may smother surfaces including food
sources and breeding substrates. High salinity may affect other ecosystems components such as
plant or macroinvertebrate composition and abundance having indirect impacts to fish feeding
and habitat.
136
Brian Deggar
Fish kill of Flathead Gudgeon after pollutants entered a creek from a winery along the North Para River at
Tanunda in April 2000 247
Silt laden runoff from a roadway entering the Onkaparinga River Gorge
137
3.4. ALIEN SPECIES & STOCKING (BIOLOGICAL POLLUTION)
Alien species is used here to describe species exotic to Australia (SA Fisheries Management Act
2007) and Australian native species translocated outside their natural range. The introduction of
organisms (biological pollution) outside their natural range is a worldwide problem in aquatic
systems with serious impacts to ecosystems and biodiversity in numerous cases, particularly in small
isolated habitats248. Fish translocated into one area have the potential to disperse more widely
through connected waterways. The problem then escalates when these established species are
more frequently encountered and further dispersed by humans. This is well illustrated by the rapid
range expansion of Common Carp in Australia which included dispersal along river systems but has
also many new isolated river basins and catchments including isolated wetlands around Adelaide.
Fish translocations can occur from a variety of mechanisms including deliberate releases (legal
or illegal) or accidental movements (list adapted from a recent Australian review249 with local
examples provided where available):
• Deliberate legal stocking (recreation or conservation): permits for trout stocking in the Mount Lofty
Ranges; attempts to form refuge populations of threatened native fishes.
• Contaminants of fish stocking (i.e. generally smaller fish that colonise aquaculture ponds and are
then transported with juveniles of angling species): species such as Carp Gudgeon and Gambusia
are potential candidates.
• Bait bucket introductions (i.e. live animals discarded after use at a different place to where
they were captured): Goldfish were suspected to be introduced via this method in the Lake Eyre
Basin 250.
• Transfers via water diversions (e.g. pipelines between river systems): several species which occur
in the River Murray may have been introduced to the Torrens and Onkaparinga catchments via
this linkage.
• Discarding of aquarium fish (and plants): Goldfish commonly occur in urban and rural
centres23,27,53.
• Escape from aquaculture facilities: marron on Kangaroo Island.
• Deliberate introductions for (a) pest control (e.g. Gambusia was distributed widely after WWII
under the perception that it was a good mosquito control agent) and (b) biodiversity
enhancement (e.g. wetland stockings251).
• Deliberate illegal stocking: many larger Australian native species including Murray Cod and
Golden Perch have been stocked into waterways outside their natural range1.
• Escape from outside ponds and farm dams close to waterways or that overflow during winter
or storms.
• Transfer on commercial fishing gear.
• Deliberate release for cultural reasons.
• Contaminants of ballast water (shipping): estuarine/marine species that can colonise
freshwater141.
A variety of fishes, invertebrates and plants have been introduced into aquatic habitats of South
Australia. This includes at least 27 alien fish species, fourteen of which have established populations
and/or are regularly stocked (Table 4). The majority of such species have been introduced in
and around Adelaide and in the Murray system. Problems with introduced organisms can be
categorised as including (a) biological interactions, (b) transfer of disease and parasites, and (c)
genetic implications. It is important to recognise that any species, exotic or native, introduced to
areas where they do not naturally occur could cause one or more of these problems.
138
Table 4. Alien species recorded in South Australia by Drainage Division1,252. Alien fishes in natural
waterways are regarded as established species (x) if their populations are self-sustaining or if they
are continually stocked, and as introduced species if records are few and isolated (I) or confined
to artificial (A) waterbodies (and potentially could become established); (*) recorded in marine
habitat; (?) unverified record.
Family
Taxon
Common name
SEC
MD
SAG
LE
WP
Carassius auratus
Goldfish
x
x
x
x
A
Cyprinus carpio
Common Carp
I
x
x
A
Tinca tinca
Tench
x
x
x
Cobitidae
Misgurnus
anguillicaudatus
Oriental Weatherloach
Salmonidae
Oncorhynchus mykiss
Rainbow Trout
Salmo salar
Atlantic Salmon
Salmo trutta
Brown Trout
Salvelinus fontinalis
Brook Trout
Gambusia holbrooki
Eastern Gambusia
Phalloceros
caudimaculatus
Speckled livebearer
Perca fluviatilis
Redfin Perch
x
x
x
I
A
x
Exotic species Cyprinidae
Poeciliidae
Percidae
I
I
x
I
I
x
x
I?
x
x
I
I
x
x
I*
x
I
I
A
x
Translocated Australian native species
Plotosidae
Tandanus tandanus
Freshwater Catfish
Galaxiidae
Galaxiella pusilla
Dwarf Galaxias
Melanotaeniidae
Melanotaenia fluviatilis
Murray Rainbowfish
Centropomidae
Lates calcarifer
Barramundi
Ambassidae
Ambassis agassizii
Agassiz’s Glassfish
Percichthyidae
Gadopsis marmoratus
River Blackfish
Maccullochella peelii
peelii
Murray Cod
I
A
x
I
Macquaria ambigua
ambigua
Murray-Darling Golden
Perch
I
A
x
A
Macquaria
novemaculeata
Australian Bass
I
I?
Nannoperca australis
Southern Pygmy Perch
A
A
Terapontidae
Bidyanus bidyanus
Silver Perch
A
A
Eleotridae
Hypseleotris sp. 1
Midgley’s Carp Gudgeon
Hypseleotris sp. 3
Murray Darling Carp
Gudgeon
Mogurnda adspersa
Southern Purple-spotted
Gudgeon
Philypnodon macrostomus
Dwarf Flathead Gudgeon
Oxyeleotris lineolata
Sleepy Cod
TOTALS
I?
I
I
A
A
I
A
x
x
A
A
x?
I
27
13
20
22
8
4
known established
5
7
13
2
0
Drainage Divisions: SEC = South East Coast, MD = Murray-Darling, SAG = South Australian Gulf,
LE = Lake Eyre, WP = Western Plateau
139
x
I?
(A) BIOLOGICAL INTERACTIONS Direct and indirect problems associated with the biology of
introduced organisms include those listed below, and are especially problematic during periods
when habitats contract and native fish are confined. Impacts may be directed to sensitive groups
or be manifested as ecosystem level impacts following the removal of certain species or resources
(trophic cascades):
• Predation: many native fishes in South Australia are small species that have evolved in stream,
spring, wetland and waterhole environments without exposure to large active predators. The
introduction of large predatory fish into such areas poses a high risk to native fish, tadpoles and
frogs, and macroinvertebrates especially decapod crustaceans (e.g. Spiny Crayfish and Yabbies).
Smaller introduced species could also prey on the eggs or larvae of native fishes.
• Competition: juveniles of larger species or smaller growing species can compete for the same
resources as native species including food but also available habitat (e.g. forcing a greater
exposure to predators).
• Aggression: territorial or aggressive behaviour can impact native species through competition for
space/habitat (above) and physical damage to individuals such as damage mucosal coat and
fins (and hence increased risk of disease or reduced condition for spawning or growth).
• Behavioural changes: the presence of introduced species may alter the behaviour of native
species feeding or foraging periods or force the use of suboptimal or non-preferred habitat.
• Habitat alteration: the feeding ecology or behaviour of introduced species may disturb
environmental conditions required by some species or ecosystems (e.g. Carp disturb sediments
and increase turbidity, remove of aquatic plants)
(B) TRANSFER OF DISEASE AND PARASITES Australia’s long evolutionary isolation (tens of thousands
to millions of years) has limited exposure to diseases (i.e. viruses, bacteria and fungi) and parasites.
Therefore local native species may have a low immunity to new forms or strains introduced from
oversees or interstate. Pathogens or disease causing agents can be primary or secondary in nature,
causing disease in healthy or minimally stressed fish and fish with compromised health respectively.
In the later case, poor environmental conditions or stress increases the susceptibility of populations
to new or existing disease which may compromise survival of remnant or refuge populations129.
Potential pathways for the introduction of diseases and parasites include:
• Fish stocking: the movement or introduction of fishes to regions, catchments or stream sections
where they do not naturally occur, especially fish that have been apart from the natural
environment, poses significant risks. This is especially true for exotic species that could carry
disease or parasites which native fish have no acquired immunity for.
• Discarded aquarium species: a multitude of tropical and temperate freshwater species are
utilised within the aquarium trade, and desired fishes are selected from around the world,
facilitated through international exchange (importation). In the order of 8-10 million fishes
are imported into Australia each year and with this comes an associated risk of importation of
other micro-organisms (disease and parasites) including ‘hidden’ infections which may avoid
detection 253,254. The intentional or accidental release of fish, water or materials from aquariums
and ponds into natural waterways thus provides an avenue for introducing disease and parasites
to native fish (and is illegal).
• Inter-basin transfers: movement of water and organisms between areas provides another
mechanism for dispersal of disease or disease carrying organisms. Pipelines such as those
between the River Murray and catchments on the western Mount Lofty Ranges are an example.
Movement of materials such as unsterilised or not thoroughly cleaned fish sampling equipment,
construction and maintenance machinery, and aquatic vegetation are all potential avenues for
transportation of disease (plus potential introductions of fish and plants).
Current and potential diseases and parasites of native fishes in South Australia are poorly studied
with little routine monitoring for new outbreaks. Potential problems include viruses such as EHNV
and Gourami Iridovirus253,255, fungal infection (e.g. Saprolegnia, Aphanomyces), bacterial
140
infections such as Goldfish Ulcer Disease (linked to Aeromonas salmonicida)256 and Fish
Tuberculosis (Mycobacteria), and parasites such as tapeworm (Bothriocephalus acheilognathi)
and Anchor worm (Learnea spp.).
(C) GENETIC IMPACTS
Two main categories of genetic impact can be considered in relation to fish introductions:
• Decline and fragmentation due to the direct impacts of introduced species. Biological
interactions may lead to reduced population size (e.g. continual predation, exclusion from
habitat, disease), population bottlenecks during critical periods, altered natural selection, and
poor connectivity and gene flow within populations – all serving to reduce genetic diversity and
uniqueness within a population.
• Reproductive interaction of local and stocked fishes. Mostly an issue with the translocation
of Australian native species where mixing (reproduction) of different genetic strains or closely
related species could lead to: (a) hybridisation and introgression (contamination with foreign
genes) interrupting natural evolutionary trajectories and having other issues such as infertility and
outbreeding depression, (b) the loss of distinct local genetic types (diversity) through swamping
with new foreign genes257, and (c) reduced genetic diversity through swamping with genetically
similar hatchery reared fish. Some relevant local examples include the risk of mixing fish from
isolated regions such as distinct species of Golden Perch occurring in the Murray-Darling system
and Cooper Creek, swamping the local genetic diversity of Murray Cod in the SA River Murray
due to stocking fingerlings, or small distance translocations across catchment boundaries
eliminating distinct genetic strains of smaller native fishes like Southern Pygmy Perch and
Mountain Galaxias.
(D) SPECIES PROFILES Brief synopsis on the range, status, history of introduction and potential
problems for introduced species in South Australia are detailed in family order (see Table 4). More
detailed information on these species can be found in broader texts or reports 89,258,259,260,261,262.
The species has been established in South Australian waterways for some time (at least early 1900s)
with evidence of continuing introductions due to a close association with humans through culture
(e.g. aquariums and ponds). Goldfish are common in the Murray and urban Adelaide but are also
spread patchily throughout all major SA Drainage Divisions. While goldfish appear harmless, there is
a potential to compete with native species for food (zooplankton, invertebrates), to modify habitats
(e.g. suspend sediments in confined habitats; feed on and remove aquatic vegetation), and most
importantly for the introduction of disease and parasites carried with their importation into Australia.
The illegal use of Goldfish as live bait poses a high risk of introducing disease to native fish stocks,
potentially ruining fishing opportunities and impacting biodiversity.
141
Goldfish
Common Carp
A species well known and much maligned by the general public, commonly referred to as
European Carp. Carp became established in the Murray system in the late 1960s where it is now
abundant and has since become established in other streams of the Western Mount Lofty Ranges
(e.g. Onkaparinga, Torrens and Light rivers) as well as numerous local wetlands in the Adelaide
region. Only isolated reports have been made from the South East and Lake Eyre Basin. The impacts
of this species appear to be interlinked with broader environmental change, as they have a high
tolerance for stable, stagnant habitats. Nevertheless, potential impacts are thought to include
their high densities providing competition with small native species for food (zooplankton) and
space, increased turbidity and loss of submerged aquatic vegetation due to their large adult size
and feeding mode, and as vectors for disease and parasites. Any impacts are most noticeable in
confined areas such as wetlands or stream pools.
Weatherloach and other potential exotic invaders
Only a few unverified records of Weatherloach have so far been made in South Australia, however
the species (a small eel like fish reaching ~20cm) has become established in the eastern states and
has undergone a rapid proliferation in the last 20 years. It is now advancing down the Murray River in
Victoria towards the South Australian border. Potential impacts from species which is highly tolerant of
environmental extremes include competition and potential predation on eggs and larvae of native
fish 263, posing particular danger to species in the Mount Lofty Ranges and Lake Alexandrina. Other
potential pest species that are established in other parts of Australia that could be a threat to local
native species and ecosystems include Tilapia, Rosy Barb, and numerous aquarium species.
142
Stomach contents of a Brown Trout in the
Finniss River catchment which includes 15 fish
(Flathead Gudgeon and Mountain Galaxias)
and numerous Glass Shrimp
Brown and Rainbow Trout
Both Brown and Rainbow Trout are active predators, often being much larger than species native to
systems where they are stocked. Many of the impacts of trout probably occur upon initial stocking (e.g.
loss of native fish populations in the Torrens265), however there is evidence of ongoing impacts to native
species such as Mountain Galaxias, Climbing Galaxias and Southern Pygmy Perch. These native species
have restricted fragmented distributions at some sites in the Mount Lofty Ranges likely attributable to the
presence of trout25,27,28,51. Trout tend to occupy stream regions or pools with better water quality and flow
and thus are in direct conflict with optimal habitat and refuge areas of native species. Trophic cascades
are also possible due to heavy feeding on invertebrate fauna and possibly tadpoles.
143
Trout have been systematically stocked into the South Australia’s waterways since the late 1800s,
especially after the 1950s. Given documented stocking locations, plus the likelihood of considerable other
releases, it is fair to say that essentially any waterbody in temperate regions of the State (and some warmer
regions) has probably received trout fingerlings at some stage. Several systems like
the Broughton, Light, Torrens, Onkaparinga, Finniss, Hindmarsh and Currency catchments (Mount Lofty
Ranges) and Mosquito Creek (SE) have each received hundreds of thousands of fingerlings over time264.
Some populations appear to recruit in the wild but many are topped up with stockings under a PIRSA
Fisheries permit system. The number of catchments stocked in recent times has been reduced mainly
due to decline in environmental conditions to the point that areas are no longer suitable to carry trout
signalling broader environmental problems, but tighter control is also being implemented.
Female
Male
Eastern Gambusia
The Eastern Gambusia (Gambusia for short) is a small fish that attains a length of less than 5cm.
It is able to rapidly expand populations, giving birth to live young. It was originally introduced for
mosquito control (especially around World War II), but is now known to be no better at controlling
mosquito larvae than the native fish and macroinvertebrates which naturally fulfil this role. The
species can negatively impact on these natural mosquito predators (hence use of the name
Mosquitofish is discouraged). It occurs widely in South Australia and is considered a threat to many
native fishes because it is aggressive, nipping at fins and the body of other fish, can predate on
eggs and young fish, and can compete for food and space (e.g. aggressively defends shallow
pool margins 39). The largest impacts are likely to occur in confined habitats such as mound springs
or isolated stream pools, or areas with sensitive small species such as Dwarf Galaxias and Pygmy
Perches. The species has high tolerance of environmental extremes and hence can be favoured by
declining environmental flows and habitat degradation.
Speckled livebearer
This species, a relative of the Gambusia, represents a newly documented invasion in South Australia
(southern Adelaide)252. Like its cousin it is known to be aggressive and compete with native species.
It has likely become established through escape or release from captive fish, and highlights the
need for vigilance with regard to alien species introductions.
144
Redfin are an introduced predatory species which threaten populations of small fish such as Pygmy Perch and Galaxias
Redfin
Compared to most small native fish, Redfin are large growing and are highly predatory (with a
large mouth). The species can breed and grow rapidly with impacts likely to include competition
for space and food (as juveniles), predation or behavioural shift forcing loss or exclusion of native
fish from important habitat. A Western Australian study found diet of Redfin between 50-200mm
comprised mostly small aquatic invertebrates, and Redfin >200mm preyed almost entirely on
decapod crustaceans and fish. The study concluded that Redfin were believed to have played a
significant role in the local extinction of three native fish species 266. This matches local observations
of potential impacts to species such as Southern Pygmy Perch, River Blackfish, Mountain Galaxias,
Yarra Pygmy Perch and Murray Hardyhead in their respective distributions in the Mount Lofty
Ranges, Lower Lakes and Mosquito Creek13,23,25,113,260. Impacts are likely to extend to Yabbies, Spiny
Crayfish and tadpoles.
145
Redfin have been spread widely in South Australia, particularly in the Adelaide region and South
East of the State. Introductions occurred soon after settlement with records of the species becoming
established in major areas such as the River Torrens and River Murray by the 1920s. They are most
common in streams of the western Mount Lofty Ranges such as the Torrens, Onkaparinga rivers,
Lake Alexandrina and some tributaries (Finniss and Angas rivers), and waterholes and streams of
the South East including Bool Lagoon (when wet). Interestingly, harsh environmental conditions in
recent years appear to have resulted in a decline in distribution and abundance in Mosquito Creek
suggesting certain vulnerabilities or intolerances118.
Native fish species
Large predatory species such as Murray Cod, Golden Perch and Freshwater Catfish are increasing
used for stockings (angling purposes) with some records of translocated fish from South Australian
waterways1. However, just because such species are native to Australia, does not mean that they
will not pose a threat to areas where they do not naturally occur. Their potentially large adult size
and predatory nature threaten small native species and invertebrates (especially Spiny Crayfish)
in areas where they are stocked or escape to (e.g. from farm dams that overflow into natural
waterways). Further, stocked fish may also carry disease from hatcheries or other areas, and there
are potential genetic implications such as hybridisation or genetic swamping of native populations.
Similarly, small native species stocked outside their natural range could compete for food and
habitat with local species, transfer disease or parasites and have implications for mixing of different
genetic strains. Stocking is seen as a way of improving declining fish populations, however it is often
a band-aid solution which fails to address the underlying threats to species such as loss of habitat.
Further, if undertaken incorrectly, stocking can cause its own problems through genetic impacts,
disease introduction, impacts to other ecosystem components and increased competition pressures
for natural populations.
Marron
NSW
Marron, native to Western Australia, is now widely established on Kangaroo Island and some
sections of the Fleurieu Peninsula. In these areas they reach a very high biomass during
concentrated conditions, and are likely to be impacting fish directly as a large aggressive animal
(e.g. predation) or alter the food-chain (e.g. competition or replacement of natural invertebrates).
The species has established over the last 20-30 years with mechanisms such as escape from ponds
or dams and illegal movements and stocking probable. There has to date been little research or
management undertaken on control of prevention of spread.
WA
NT
Qld
SOUTH AUSTRALIA
NSW
Vic.
Location map
-Alien species mapMarron
ADELAIDE
(Cherax cainii)
! Record location
!!!! ! ! !!
! !
!! !
!!
! !
!
!!
!
!
!!
! !
! !
!!
State outline
Waterway
!
Inland waterbody
Coastline
0
40
80
120
km
¯
Willows
Willows comprise a number of species of deciduous water loving trees which can spread to line and
choke small waterways and exclude native plants. Willows also have a heavy rapid leaf drop with
fast decomposition which can lead to deoxygenation and poor water quality and smothering of
underwater surfaces and vegetation. However, in some cases Willows now represent the only shade
and sources of cover at some degraded sites and actually provide important habitat for species
with requirements for cool conditions such as River Blackfish, Southern Pygmy Perch, Mountain
Galaxias and Climbing Galaxias in the Mount Lofty Ranges. The sometimes crude methods used to
control Willows involving heavy physical disturbance to stream edges and a subsequent transition
from full to no shade can be a threat to native fish populations and a more gradual transition to
native riparian vegetation is recommended.
146
3.5. EXPLOITATION (USE)
Catch and use of fishes occurs for a variety of purposes including recreational, commercial and cultural
reasons (e.g. food, angling), for research, biodiversity enhancement projects (e.g. collecting fish for
stocking wetlands) and for personal enjoyment or observation such as keeping native fish in aquariums.
These uses can provide an appreciation of the intrinsic value of native species and a greater awareness
and knowledge of their natural history and biology. However, the inappropriate or excessive use of native
fish populations could provide an additional stress to threatened species and those with temporarily
restricted distributions.
(A) REDUCED ABUNDANCE Use can ultimately reduce the abundance of species at a point in time or
progressively. This has the potential to impact on the number of fish or critical mass required to sustain
a population or basic levels of genetic diversity (e.g. appropriate number of spawning fish). Species
vulnerable to exploitation include those with highly restricted ranges (e.g. desert fish32, Pygmy Perches),
which spawn infrequently or are slow growing, and species which occur in concentrated refuges during
dry periods (e.g. larger fish of the Lake Eyre Basin in systems like Coopers Creek and the Neales River).
Other species are susceptible to over harvest during spawning aggregations or migration.
Preparing a large catch of Murray Cod, a top order predator, caught at Renmark 1898. Photo courtesy of
the State Library of South Australia (SLSA: B45136)
147
(B) TROPHIC CASCADES Fish play a variety of roles in ecosystems such as being an important part or link
in food chains. Nearly all small native species and juveniles of larger native species are carnivorous and
hence consume aquatic and terrestrial macroinvertebrates and crustaceans. A particular aspect of this
predation includes a role in mosquito control (by predation on wrigglers or adult mosquitoes). Small fish
are in turn consumed by predators such as birds, water rats and larger fish. Larger predators potentially
control the dynamics of other species (keystone species). Such food chains exist in a fine balance with
environmental conditions, and hence the selective removal of certain species, especially larger predatory
species like Murray Cod, may indirectly alter the composition of a local fauna by allowing the proliferation
of certain smaller species (‘top-down’ ecosystem effects). Alternately the introduction of larger predators
could eliminate small species but leave the food they previously were feeding on (for example leaving
no natural predators of mosquito wrigglers in pools as has been observed with trout in the Mount Lofty
Ranges25. The selective removal of a species through legal or illegal fishing effort could mean that another
species takes its role in a system, so that efforts to recover the exploited species later on are less successful
as it has been functionally replaced. This is an example of an altered ecosystem state.
3.6. POPULATION DECLINE
A grouping of other potential threats relate to the current characteristics of populations and
social and political factors. These are very much cumulative or interlinked with problems such as
hydrological alteration or habitat loss but warrant specific inclusion and highlight.
(a) Loss of genetic diversity Genetic diversity is the backbone to biodiversity or the number
of unique animals and plants that have evolved and occupy habitats in South Australia. Genetic
diversity can be expressed on a number of levels including phylogenetic (deeper relationships
such as Families and Genera), species boundaries, and within species variation. Within species
variation can provide an ability to adapt to changing environmental conditions, and can relate to
variability both between and within different populations of a species. For example, the Southern
Pygmy Perch has distinct genetic lineages in the South East and Murray regions of the State, and
individual catchments in the Mount Lofty Ranges harbour unique genes and frequencies of different
genes (heterogeneity). These distinguish each pygmy perch lineage and form the basis of potential
adaptation or evolution in their isolated habitats13,22. Processes that can erode genetic distinctness
or within population/species variation include local extinctions or range contractions (e.g. from
habitat loss), bottlenecks from low numbers of fish at a point in time (e.g. over harvest during
drought), fragmentation (e.g. artificial barriers), and swamping with hatchery reared fish.
(b) Restricted range Many species or populations of threatened species have a limited area of
occurrence. This can be due to natural isolation such as desert fish restricted to a particular stream
(Flinders Ranges Purple-spotted Gudgeon) or group of artesian springs (e.g. Dalhousie endemics),
or alternately species which were formally more widely spread but have contracted due to human
related impacts like hydrological alteration. Good examples include River Blackfish in the River
Murray drainage, a once widespread species that now occurs as four small populations, including
one which is restricted to two refuge pools25,267. Spatially restricted species and populations face
a variety of challenges for long-term survival. Any change in their habitat could be devastating,
and changes to small areas could happen quite easily and quickly through both chance natural
conditions (e.g. floods and drought) and threatening processes such as habitat change, species
introduction, pollution events and water quality issues247, and loss of flow. Any new small change
cumulative to existing threats may push a population past sustainable limits.
(c) Management and planning Being hidden below the waters’ surface, most native fish do
not have a high profile in the community or among planners, land and resource managers, and
developers. This is particularly the case for small, rare fish with no recreational fishing value. A
general lack of awareness of species or regional faunas is a threat to South Australia’s freshwater
fishes because:
• Lack of action: a failure to address the specific conservation requirements or actions for
threatened species or communities could lead to species loss.
• New threats: the requirements and conservation of native fish may not be considered during new
developments or changes in landuse, and in restoration programs.
• Limited funding: fish may not receive the same levels of attention or priority in restoration and
management, leading to few dedicated actions and a greater risk of species loss from the State.
• Limited research: there may be a tendency for limited research and monitoring leaving
knowledge gaps on the presence or condition of ecological assets as targets for conservation
and management and biological information available for management.
• Legislative protection: the importance of protecting fish populations, their habitat and flow
processes has been (and is currently) poorly represented in State laws and regulations. This has
particularly been the case for small species that tend to fall between the gaps of terrestrial
species conservation and fisheries management.
148
3.7. CLIMATE CHANGE
The projections of climate change as a result of current and increasing world-wide green house gas
emissions have considerable relevance for South Australia. Exact predictions are difficult given large
temporal variations in climatic conditions, and with variations for different parts of the State, but
the overall trend based on average seasonal and annual conditions suggests South Australia will
become hotter and drier, with a change in the nature of rainfall events268.
Notably in time, the prevailing low pressure systems from the south west which produce rainfall in
the southern areas of the State, are projected to decrease in number but increase in intensity with
an overall effect of less rain in more concentrated events, particularly in spring. The northern half
of the State is predicted to become warmer (e.g. between 1 to 6°C) with an increasing frequency
and magnitude in summer rainfall events (e.g. more floods). A summary of predicted changes in
rainfall and temperature are contained in Figure 16. Broader changes are also likely to affect South
Australia especially in the Murray-Darling Basin where with less rain, flow to South Australia could be
further reduced.
Sights like this concentrated refuge pool could become more common with reduced rainfall and higher
temperatures, combined with existing water use
149
Climate change has the potential for direct impacts along with an overarching role in exacerbating
many existing threats. A change in climate could mean aquatic habitats are increasingly
influenced by disturbance events of large floods and longer periods of drought, and overall
warmer water temperatures and lower average flows (the latter could also result in increased
concentrations of salt, nutrients and pollutants). This pattern is likely to be further intensified in
developed regions as humans react to secure water supply with cumulative additions to existing
abstractions (e.g. dams, groundwater pumping). All fishes will be susceptible to changes in their
habitat extent and conditions (e.g. habitat loss, water quality tolerances), but those living in
currently cooler and more predictable seasonal environments will be hardest hit (e.g. cool water
species from the Mount Lofty Ranges and South East).
Figure 16. CSIRO climate change projections for South Australia covering (a) average seasonal and
annual warming ranges (oC) for around 2030 and 2070 relative to 1990 and (b) average seasonal
and annual rainfall change (%) for 2030 and 2070 relative to 1990. The coloured bars show ranges
of change for areas with corresponding colours in the maps (reproduced with permission from
McInnes et al. 2003 268).
150

Section 3 overview of potential threats

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